This invention relates to a method for making an aluminum-containing ferroally, which is suitable for use as deoxidizer in manufacturing steel.
In a conventional method where aluminum is employed as a deoxidizer in manufacturing steel, aluminum is added to molten steel in a ladle. This method suffers, however, from the disadvantage that because the specific gravity of aluminum is lower than that of the molten steel, aluminum surfaces so that the efficiency of deoxidization is not only poor but is very inconsistent. In order to overcome this disadvantage, several methods have been practised, such as these in which aluminum shaped in the form of cannon balls is shot into the molten steel with, for example, compressed air, or, aluminum cased with a metal or metals having higher specific gravity is employed. These methods are, however, all disadvantageous in that they require numerous devices and employ complicated means for adding aluminum.
Recently, for the purpose of solving the problems stated above, additive alloys have been developed which, while being composed of silicomanganese or ferromanganese (substances conventionally added to steel for adjusting the composition thereof), additionally contain aluminum. Such additive aloys have higher specific gravities and work to increase deoxidization efficiencies.
There are two methods for making such additive alloys, one being the method where solid masses of aluminum are added to molten ferroally such as silicomanganese, ferromanganese or the like, the other being the method in which aluminum shots (small solid particles of aluminum) are mixed with powders or small particles of a ferroalloy and the mixture is subjected to pressure moulding with a suitable amount of binder to give it the form of briguettes.
The former method however is disadvantageous in that the aluminum surfaces because the specific gravity of the added aluminum is lower than that of the molten ferroalloy so that only an extremely small amount of aluminum is incorporated into the product alloys, a high degree of segregation of the aluminum occurs in the ferroalloy and the cost of manufacturing the product is increased.
The latter method also suffers from the disadvantage of high cost since briguetting requires equipment to carry out a number of processing steps including fragmentation and sizing of the aluminum and ferroalloy to make them suitable in size for briguetting, addition of binder, and pressure-molding with a pressure-molder.
Thus, although aluminum-containing ferroalloy is known to work as a deoxidizer of high efficiency and further to stabilize compositions of steels only by simple addition thereof to the steel, it has not received full practical application since it is difficult to make the same at low cost and with a high degree of homogenuity.